Hilda Cohen with the group "Make Brooklyn Safer" helped put up the signs.

"This is not anti-car, it's pro-people," Cohen said.

NYC's Department of Transportation will remove unauthorized signs. The department and Mayor Bill de Blasio are pushing for lower limits.

"As noted throughout the Vision Zero report and reiterated in recent testimony at Transportation Committee hearings, DOT is committed to installing additional slow zones and working with stakeholders across the city and in Albany to lower New York City's speed limit," said a DOT spokesperson.

The city is working with neighborhood groups to complete 15 new slow zones by the end of next year and add 25 more .